Exchange protein directly activated by cAMP (Epac) 1 plays an essential role in stress-induced exercise capacity by regulating PGC-1α and fatty acid metabolism in skeletal muscle.

Exchange protein directly activated by cAMP (Epac) mediates cAMP-mediated cell signal independent of protein kinase A (PKA). Mice lacking Epac1 displayed metabolic defect suggesting possible functional involvement of skeletal muscle and exercise capacity. Epac1 was highly expressed, but not Epac 2, in the extensor digitorum longus (EDL) and soleus muscles. The exercise significantly increased protein expression of Epac 1 in EDL and soleus muscle of wild-type (WT) mice. A global proteomics and pathway analyses revealed that Epac 1 deficiency mainly affected "the energy production and utilization" process in the skeletal muscle. We have tested their forced treadmill exercise tolerance. Epac1-/- mice exhibited significantly reduced exercise capacity in the forced treadmill exercise and lower number of type 1 fibers than WT mice. The basal protein level of proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) was reduced in the Epac1-/- mice. Furthermore, increasing expression of PGC-1α by exercise was also significantly attenuated in the skeletal muscle of Epac1-/- mice. The expressions of downstream target genes of PGC-1α, which involved in uptake and oxidation of fatty acids, ERRα and PPARδ, and fatty acid content were lower in muscles of Epac1-/-, suggesting a role of Epac1 in forced treadmill exercise capacity by regulating PGC-1α pathway and lipid metabolism in skeletal muscle. Taken together, Epac1 plays an important role in exercise capacity by regulating PGC-1α and fatty acid metabolism in the skeletal muscle.

Characterization of a novel cellular retinoic acid/retinol binding protein from shrimp: expression of the recombinant protein for immunohistochemical detection and binding assay.

Members of the cellular retinoic acid (CRABP) and retinol binding (CRBP) proteins family are involved in the metabolic pathways of retinoic acid (RA) and retinal respectively. The objective of this study is to determine whether such proteins are present in crustaceans. We report here the cloning and isolation of a novel complementary DNA (cDNA) that showed characteristics of the CRABP/CRBP from the ovary and eyestalk of the shrimp. The cDNA is 0.9 Kb in size and the deduced shrimp protein is encoded for a protein of 14 kDa. Although it shows high amino acids sequence similarity to both the vertebrate and invertebrate CRABP, some conserved amino acids identified in other CRABPs were not found in MeCRABP. MeCRABP is expressed in the ovary, eyestalk, testis, epidermis and early larvae. The presence of MeCRABP in early larval stages suggests that the protein may be involved in the early larval development. Recombinant MeCRABP was produced and used to generate a polyclonal antibody. In the immunohistochemical detection study, anti-rCRABP antibody recognized the presence of CRABP in several cell types of the eyestalk as well as the smaller oocytes of the ovary. Although MeCRABP messenger RNA transcripts can be detected in the ovary throughout the ovarian maturation period, CRABP was detected only in the primary oocytes of the ovary. The results suggest that CRABP transcripts in the mature ovary are not translated and may be supplied to the oocyte as maternal messages. The binding property of the recombinant MeCRABP was also tested by a fluorometeric method. The result indicates that rMeCRABP binds to both RA and retinal with similar affinity. This study represents the first cloning and characterization of a cDNA that belongs to a member of retinoid/fatty acid binding protein family in crustaceans.